IC Chip Coating Material and Vacuum Fluorescent Display Device Using Same

ABSTRACT

An IC chip coating material includes first metal oxide particles; a metal alkoxide; an organic solvent; and second metal oxide particles and/or flat particles of a composite oxide, the second metal oxide particles having a composition identical to or different from that of the first metal oxide particles and also having a mean particle size and/or a shape different from that of the first metal oxide particles. Further, a vacuum fluorescent display device includes an IC chip, wherein the IC chip is at least partially coated by a coating material layer including the first metal oxide particles; a metal forming metal alkoxide; and the second metal oxide particles and/or flat particles of a composite oxide.

FIELD OF THE INVENTION

The present invention relates to a vacuum fluorescent display device inwhich an IC chip is mounted on a vessel; and, more particularly, to avacuum fluorescent display device in which an IC chip and at least apart of vicinities thereof are coated with an IC chip coating materialfor a fluorescent display device.

BACKGROUND OF THE INVENTION

As for a fluorescent display device having a chip in glass structure(hereinafter, referred to as CIG structure) in which an IC chip, i.e.,integrated circuit devices on a semiconductor substrate, is fixed on aglass anode board serving as a part of an envelope, there is known adevice which protects an IC chip from external light or the like with anIC cover formed of, e.g., 426 alloy.

However, in case of using the IC cover, there is a limit in narrowing agap between a filament and an anode. Particularly, in case of a lowvoltage operation, it is difficult to narrow an FH (distance between thefilament and the anode), thereby making it difficult to attain a highlevel of brightness.

Further, in case where the IC cover is installed, conductive materialsgenerated during a welding splash process or the like adhere between abonding wire and its neighboring wire to thereby cause a short-circuittherebetween. As a result, there may be generated an IC malfunction or adisplay fault. In order to solve the above problems, Japanese Patent No.3553868 provides a technique for coating an IC chip covered by an ICcover or a bonding wire portion with a coating material.

As shown in FIG. 9, in a fluorescent display device 50 disclosed inJapanese Patent No. 3553868, an IC chip 71 is fixed on a substrate 51 bya die bonding paste via a black insulating film 52, and a firstelectrode on the substrate 51 and a second electrode on the IC chip 71are connected to each other by a wire. Further, an insulating layer 72is formed to cover the first and the second electrode and the wire.After a lead frame as a metal element for unifying a filament support 53or the like is disposed above the IC chip 71, the substrate 51 and glassvessels 60 and 61 are sealed by fritted glasses 62A and 62B, therebyforming an envelope. Furthermore, the second electrode of the IC chip 71and the wire are coated with a coating material 74 containing insulatingparticles 73, wherein a mean particle size thereof is smaller than orequal to one third of a pitch between neighboring wires.

In Japanese Patent No. 3553868, the coating material 74 for coating theIC chip and its neighboring portion is obtained by dispersing Al₂O₃serving as insulating particles 73 into a solution where Al alkoxide asa solute is dissolved in alcohol. Here, a mean particle size of Al₂O₃ isknown to be 1 μm, and a weight ratio of Al₂O₃ to Al alkoxide is set tobe 0.5. In addition, by heating the coating material 74 under anatmosphere of 480° C., alcohol contents therein are evaporated and,then, an insulating layer 72 of Al₂O₃ is formed from an Al alkoxide by abaking process. Since the insulating particles 73 made of Al₂O₃ are notshrunk by the heating, the coating material 74 including the insulatinglayer 72 and the insulating particles 73 is less shrunk than the casewhen it is exclusively composed of a coating insulating layer during thebaking process, thereby reducing a stress applied to the wire.Accordingly, there is disclosed a technique for preventing the wireitself from being cut off or preventing the connection between the wireand the electrode from being cut.

Alternatively, the coating material 74 may be obtained by dispersingSiO₂ serving as insulating particles into a solution where polyimideresin as a solute is dissolved in dimethylacetamide. Here, a meanparticle size of SiO₂ is known to be 5 μm, and a weight ratio of SiO₂ topolyimide resin is set to be 1 (that is, a weight ratio of SiO₂ topolyimide resin is set to be 1:1). If a heating temperature is lowerthan 400° C., the coating material 74 has no degassing effect.Therefore, there is disclosed a technique for generating the insulatinglayer 72 formed of a polyimide film by performing the baking process ata temperature ranging from 400° C. to 500° C. such that the insulatingparticles 73 of SiO₂ will be made to be adhered between wires andbetween the wire and the black insulating film 52 with the use of theinsulating layer 72.

As for a fluorescent display device having the CIG structure in whichonly parts where bonding wires are connected are coated, there is knowna device disclosed in Japanese Patent Laid-open Application No.2003-132824, for example.

As illustrated in FIG. 10, in the fluorescent display device disclosedin Japanese Patent Laid-open Application No. 2003-132824, an IC chip 82is mounted on a glass substrate 81 by a die bonding paste, and a wiring83 made of aluminum or the like is formed thereon. Further, eachelectrode of the IC chip 82 and the wiring 83 corresponding thereto areconnected by a bonding wire 84. And also, the electrodes, to which thebonding wires 84 are connected, of the IC chip 82 on the substrate andthe bonding wires 84 connected to such electrodes are coated by acoating material 85.

In the fluorescent display devices having such CIG structure, by coatinga whole or a part of a front surface of the IC chip 82 with a coatingmaterial, it is possible to overcome a malfunction of the IC chip, whichis caused by a short-circuit due to a conductive foreign substanceconnecting the bonding wire 84 with its neighboring wire.

However, in the fluorescent display device of the aforementionedJapanese Patent No. 3553868, a passageway of a gas generated from thedie bonding paste for fixing the IC chip 71 is blocked by the coatingmaterial 74. Consequently, an adhesive strength of the coating material74 deteriorates and the IC chip 71 is separated from the glass substrate51 in worst cases, thereby deteriorating a performance and a reliabilityof the fluorescent display device.

Further, in the fluorescent display device of Japanese Patent Laid-openApplication No. 2003-132824, in order to solve the aforementioneddrawbacks, the coating material 85 for coating the electrodes, to whichthe bonding wires 84 are connected, of the IC chip 82 on the substrateand the bonding wire 84 connected to the corresponding electrode isprovided. As a result, the amount of gas generated is reduced by halfand, also, the passageway of the generated gas is secured. However, thegas is still discharged from the coating material 85 at the parts wherethe bonding wires are connected, and the device will face the sameproblems as those of Japanese Patent No. 3553868.

The coating material used in the aforementioned Patent documents needsto be baked at a temperature higher than 400° C. to 500° C., which leadsto a breakdown of the IC chip. Although a coating material in whichpolyimide resin is dissolved in a solvent is used, such coating materialwill shrink significantly while being cured during the drying process orthe baking process and may develop a crack or a peeling. Further, sincethe coating material described above is made of oxide of a singleparticle, the particles in a bulk formed are cured in a most closelypacked structure. As a result, there is a problem that a stress is notrelaxed and the crack or the peeling may be developed.

In case the IC chip or the like is coated with a coating material formedof a highly insulating oxide instead of the coating material describedabove, since most colors of the coating material range from white to dimbrown, the coating material is noticeable in the fluorescent displaydevice in which an insulating layer formed of an insulating materialsuch as a lead glass or the like is coated, wherein the lead glass iscolored by a paint added with oxide particles of Fe/Cr.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide ahigh-quality fluorescent display device having a highly reliable CIGstructure by coating an IC chip fixed by a die bonding paste hardlygenerating gas and at least a part of its neighboring area.

In accordance with a preferred embodiment of the present invention,there is provided an IC chip coating material including: first metaloxide particles; a metal alkoxide; an organic solvent; and second metaloxide particles and/or flat particles of a composite oxide, the secondmetal oxide particles having a composition identical to or differentfrom that of the first metal oxide particles and also having a meanparticle size and/or a shape different from that of the first metaloxide particles.

In accordance with another preferred embodiment of the presentinvention, there is provided a fluorescent display device including anIC chip, wherein the IC chip is at least partially coated by a coatingmaterial layer including first metal oxide particles; a metal formingmetal alkoxide; and second metal oxide particles and/or flat particlesof a composite oxide, the second metal oxide particles having acomposition identical to or different from that of the first metal oxideparticles and also having a mean particle size and/or a shape differentfrom that of the first metal oxide particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodiments,given in conjunction with the accompanying drawings, in which:

FIG. 1 is a partially cutaway perspective view of a fluorescent displaydevice having a CIG structure in accordance with the present invention;

FIG. 2 shows a fragmentary sectional view of an IC chip portion of FIG.1;

FIG. 3 provides a fragmentary sectional view depicting a state where anIC chip coating material for a fluorescent display device is coated onthe IC chip and its neighboring area after die-bonding the IC chip;

FIG. 4 illustrates a graph showing an exemplary test data on an IC chipcoating material for use in the fluorescent display device in accordancewith the present invention;

FIG. 5A provides a schematic diagram of an example in which the IC chipcoating material in accordance with the present invention is applied tothe IC chip and its neighboring area; FIG. 5B presents a schematicdiagram of an example in which the IC chip coating material inaccordance with the present invention is applied to a part of the ICchip and a part of a bonding wire; and FIG. 5C represents a schematicdiagram of an example in which the IC chip coating material inaccordance with the present invention is applied to a part of the ICchip conducted by connecting bumps;

FIG. 6 presents a schematic diagram of a test example for testing aninsulating level of the IC chip coating material for use in thefluorescent display device in accordance with the present invention;

FIG. 7 represents a graph showing a test result of VI characteristics ofa IC chip coating material including Fe, Cr and Mn as a main componentthereof and another IC chip coating material including Fe and Cr as amain component;

FIG. 8 depicts a graph illustrating an order of stability in anoxidation/deoxidation of metal oxide particles for use in the presentinvention;

FIG. 9 offers a fragmentary sectional view of principal parts of theconventional fluorescent display device having a CIG structure; and

FIG. 10 sets forth a sectional view of an IC chip portion of theconventional fluorescent display device having the CIG structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

First of all, a vacuum fluorescent display device of the presentinvention will be described with reference to FIGS. 1 to 5. A vacuumfluorescent display device 1 of a CIG structure in accordance with thepresent invention is an anode substrate 11 in which a wiring conductor13 of the fluorescent display device 1 and an anode 12 containing ananode conductor 14 and a phosphor layer 15 are arranged.

The anode substrate 11 is generally made of a glass substrate and aninsulating layer 26 is formed on an approximately entire surfacethereof. Moreover, an IC chip 16 is fixed to an end portion of the anodesubstrate 11 via a die bonding layer 23. The IC chip 16 is connected toa terminal 17 connected to an end portion of the wiring conductor 13 bya bonding wire 18. Further, a filament-shaped cathode 21 separated froma grid 20 by a predetermined regular distance is tightly stretched onthe anode substrate 11, while the grid 20 separated from the anode 12 bya predetermined regular distance is arranged to face the anode 12.

The anode 12 and the grid 20 are connected to the IC chip 16 by thewiring conductor 13 and also to an external lead 19 serving as an inputterminal of the IC chip 16. Further, the die-bonded IC chip 16 and itsneighboring area are coated with an IC chip coating material 25A for afluorescent display device. Furthermore, a box-shaped vacuum vessel 22is provided such that it covers an electrode on the anode substrate 11,wherein the vacuum vessel 22 is sealed by a sealing member whose maincomponent is a fritted glass having a low melting point.

The following is a detailed description of the neighboring area of theIC chip 16. As shown in FIG. 2, in order to bond the IC chip 16 to theanode substrate 11, the die bonding paste 23A needs to be adhered ontothe anode substrate 11 or onto a backside of the IC chip 16 and, then,the IC chip is mounted on the substrate at a position to be fixed. Next,a die bonding paste 23A is dissolved with the heat, thereby fixing theIC chip to the substrate. In other words, the IC chip 16 is bonded tothe anode substrate 11 via the die bonding layer 23.

Here, the die bonding paste 23A used in this embodiment will bedescribed. The die bonding paste 23A is formed of a vehicle containingfine conductive particles and an organic metal. As for the fineconductive particles, flake-shaped Ag particles whose particle sizeranges from 0.1 μm to 50 μm are used. An organic metal compoundcontaining metal atoms such as Ti, Al, Si, In, Zr or the like isgenerally liquid or soluble to a solvent. Also, it can be soaked tothereby become a paste. Further, as for the organic metal compound, itis known to form a metal oxide by using a pyrolysis reaction. Thus, theAg particles serving as a functional material in the paste can be fixedto the substrate during the baking process.

Hereinafter, a specific compound of the die bonding paste will bedescribed.

-   -   Organic titanium (TOG): 30 g    -   Conductive particles (Ag particles): 70 g    -   Organic solvent of low boiling point (tridecyl alcohol,        terpineol): proper quantity

Since the tridecyl alcohol and terpineol serving as the organic solventhave comparatively low boiling points, respectively, a very littleamount of unnecessary gas is discharged during the formation of thecoating material. Moreover, a very little amount of unnecessary gas isdischarged after the formation of the fluorescent display device iscompleted.

As depicted in FIG. 3, after the IC chip 16 is die-bonded, in order tocoat the IC chip 16 and the bonding wire 18 installed on the substrate,the coating material layer 25 made of the IC chip coating material 25Afor a fluorescent display device is formed exactly in a same way as thefixed IC chip 16 and its neighboring area are coated by using adispenser.

Hereinafter, components of the IC chip coating material for afluorescent display device used in this embodiment will be described indetail. The IC chip coating material of this embodiment is a paste madeby mixing fine particles of black tone metal oxide including Fe, Crand/or Mn as a main component thereof and for coating the anodesubstrate 11 (or white tone the metal oxide may include Al₂O₃ as a maincomponent thereof in case the insulating layer 26 is white tone); anAl₂O₃-based metal alkoxide (hereinafter, referred to as an alumina solsolution) serving as a metal alkoxide added as a fixing material; and anorganic solvent (having a boiling point ranging from about 100° C. to250° C. and non-volatile at room temperature) for making the IC chipcoating material 25A in a form of a paste. Also, mixed into the paste inaddition to the those described above are fine particles of anothermetal oxide having a composition identical to or different from that ofthe above-described metal oxide and also having a mean particle sizesand/or a shape different from that of the above-described metal oxide;and/or flat fine particles of a highly insulating composite oxide suchas mica or the like.

In case black oxide pigment of Fe, Cr and/or Mn is used as the finemetal oxide particles and fine Fe, Cr and/or Mn oxide particles of amean particle size different from that of the fine metal oxide particlesare used, the paste assumes black appearance. On the other hand, in casewhite oxide pigment of Al is used as the fine metal oxide particles andfine Al oxide particles of a mean particles size different from that ofthe fine metal oxide particles are used, the paste assumes whiteappearance.

Moreover, a Si oxide can be used as a white metal oxide pigment whilethe Si oxide is used as another fine metal oxide particles having adifferent mean particle size. Further, depending on the purpose of usingthe fluorescent display device 1, a contrast can be expressly emphasizedintentionally by using the white tone fine metal oxide particlesincluding Al₂O₃ as a main component thereof in case the insulating layer26 is black, and the black tone fine metal oxide particles including Fe,Cr and/or Mn as a main component thereof in case the white insulatinglayer 26 is white.

In order to relax a stress caused by a drying process during theformation of the coating material layer 25 generated by coating acorresponding material, the IC chip coating material 25A includes, inaddition to first fine metal oxide particles, second fine metal oxideparticles and/or flat fine particles of a highly insulating compositeoxide, the second metal oxide particles having a composition identicalto or different from that of the first metal oxide particles and alsohaving a mean particle size and/or a shape different from that of thefirst metal oxide particles. Further, a mean particle size ratio of thefirst fine metal oxide particles to the second fine metal oxideparticles and/or flat fine particles of the highly insulating compositeoxide is preferably set to be 1:5 or more (for example, in case a meanparticle size of the first fine metal oxide particles is about 3.5 μm,that of the second fine metal oxide particles and/or the flat fineparticles of the highly insulating composite oxide is about 25 μm).

Moreover, since the dispenser may be blocked by the fine particles usedherein during the coating process, it is preferable to restrict a meanparticle size of the added fine particles to be 1/10 of an innerdiameter of the dispenser used for the coating process (e.g., if theinner diameter of the dispenser ranges from 0.3 mm to 0.5 mm, theparticle size of the fine particles is preferably from 30 μm to 50 μm).

Besides, in case the flat fine particles of the highly insulatingcomposite oxide are added, the added amount is preferably about 20% of atotal amount of the fine metal oxide particles and the fine particles ofthe highly insulating composite oxide in the IC chip coating material25A. Further, the flat fine particles of the highly insulating compositeoxide is not limited to the aforementioned mica as long as they areinsulating particles of a mean particle size and/or a shape differentfrom that of the added fine metal oxide particles and do not affect theperformance of the IC chip coating material 25A.

As for the metal alkoxide (having at least one M-O—C combination, Mbeing a metal) added as a fixing material, there are TiO₂-based metalalkoxide, SiO₂-based metal alkoxide and the like in addition to thealumina sol solution. Since, however, an insulating characteristicthereof increases in the order of TiO₂, SiO₂ and Al₂O₃, in case ofTiO₂-based metal alkoxide, if there is a more stable oxide (alumina orthe like) than the TiO₂-based metal alkoxide, it is deoxidized during aheating process of the fluorescent display device 1, thereby decreasingits original resistance. In such point of view, it is preferable to useAl₂O₃-based metal alkoxide.

As for the organic solvent for making the IC chip coating material 25A apaste, it is preferable to use an organic solvent whose boiling pointranges from about 100° C. to 250° C. This is because if the boilingpoint is low while using the dispenser, the organic solvent becomes dryinside a cylinder or near a nozzle and thus blocks the dispenser.Further, it is difficult to achieve a proper coating state. On thecontrary, if the boiling point is high, a vacuum level deteriorates orit will have ill effects on an emission in the manufacturing process ofthe fluorescent display device. As a result, the boiling point of theorganic solvent used herein preferably ranges from about 100° C. to 250°C.

Although a film thickness obtained by coating the IC chip 16 and itsneighboring area with the IC chip coating material 25A configured asdescribed above varies depending on coating areas, it is greater than athickness of the IC chip 16 by 50 to 150 μm on the IC chip 16 (thethickness of the IC chip 16 being about 0.2 mm to 0.3 mm). Further, asshown in FIG. 3, the film thickness of the IC chip coating material 25Anear a top of the wire is controlled within the range of 150 μm±100 μm.

In case the IC chip coating material paste 25A is coated and then driedat about 100° C. to 250° C., an expansion coefficient ranges as follows:

glass substrate (soda lime glass): about 90×10⁻⁷/° C.;

IC chip (Si wafer): about 40×10⁻⁷/° C.; and

wire: about 200×10⁻⁷/° C.,

wherein a thermal expansion coefficient of the IC chip coating material25A is preferably of an intermediate value between that of the IC chip16 and that of the glass substrate.

Further, as illustrated in FIG. 4, since the alumina sol serves as afixing material, as the amount of the fixing material decreases, astress generated becomes small and a stress inclination relative to acoating film thickness becomes small, too.

Along with the reduction of the alumina sol, the adhesive strength forsupporting the IC chip coating material 25A on the anode substrate 11 isreduced. Furthermore, in case the amount of alumina sol is extremelylarge, it does not become a paste. In case an alumina powder added tothe alumina sol solution has a single particle size and the coating filmbecomes thick, the stress cannot be relaxed so that cracks aredeveloped. However, by adding particles of a different particle size,the stress can be relaxed by fine cracks generated between twoparticles.

In other words, it is preferable to reduce the amount of alumina solsolution added up to a level capable of reducing the stress with aproper adhesive strength and then add particles of a different particlesize.

As for the coating method of the IC chip coating material, asillustrated in FIGS. 3 and 5A, it is preferable that the IC chip and itsneighboring area are entirely coated, but the coating method is notlimited thereto. In other words, even if the IC chip coating material25A is partially coated over only the portions where the coating processis required on the IC chip 16 and its neighboring area, the same effectsof the coating method described above can be achieved. For example, asshown in FIG. 5B, it is possible to coat partially one side of the ICchip 16. In addition, as depicted in FIG. 5C, in case the fluorescentdisplay device has connecting bumps 17 a and 17 b formed to face thesubstrate 11 and the IC chip 16, respectively, the connecting portionthereof can be exclusively coated by the IC chip coating material 25A,as illustrated.

And also, in case the IC chip is entirely coated, for securing astability against an inferior insulation, it is preferable to use the ICchip coating material 25A using black fine metal oxide particlesincluding Fe, Cr and/or Mn as a main component thereof, which have a lowlevel of a thermal stress than the IC chip coating material 25A usingwhite fine metal oxide particles including Al₂O₃ as a main componentthereof.

First Preferred Embodiment

Hereinafter, the fluorescent display device 1 having the CIG structurein accordance with the present invention will be described in detailbased on the manufacturing process. The present invention is not limitedto following embodiments, and various changes and modification may bemade without departing from the scope of the invention.

First of all, the anode substrate 11 on the inner surface of which thewiring conductor 13 and the anode conductor 14 are patterned isprovided. Further, by adhering the phosphor layer 15 on a top surface ofthe anode conductor 14, the anode 12 is formed. Furthermore, the grid isdisposed above the anode 12 at a position upwardly separated by apredetermined regular distance therefrom, and the filament-shapedcathode 21 is tightly installed above the grid 20 at a position upwardlyseparated by a predetermined regular distance therefrom.

Moreover, the die bonding paste 23A is coated on the grounded electrode24 provided at an end portion of the anode plate 11 provided with thephosphor layer 15 or directly on a top surface of the plate 11. Next, asshown in FIG. 2, the IC chip 16 is mounted on the anode plate 11 andthen dried at about 200° C. Further, the bonding wire 18 connects the ICchip 16 to the terminal 17 connected to the anode 12 and the grid 20 bythe wiring conductor 13 while another bonding wire connects the IC chip16 to the terminal 17 connected to the external lead 19 by the wiringconductor 13.

The die bonding paste used herein is obtained by mixing organic titanium(TOG) of 25 g, fine conductive particles (Ag particles) of 75 g and apredetermined proper quantity of a solvent (terpineol).

Further, after the IC chip 16 is die-bonded, as shown in FIG. 3, the ICchip 16 on the anode plate 11 and its neighboring area are coated withthe IC chip coating material 25A.

The IC chip coating material 25A used herein is a paste obtained bymixing following materials:

(1) black fine metal oxide particles including Fe, Cr and Mn as a maincomponent thereof (Fe₂O₃: about 40%, Cr₂O₃: about 45% and MnO₂: about15%), whose particle size is about 3.5 μm: 55 g;

(2) flat fine particles of a composite oxide, i.e., mica whose particlesize is about 25 μm: 10 g;

(3) alumina sol as a fixing material: 10 g; and

(4) ethylene glycol as a solvent: 25 g.

After the coating process is completed, a drying process is performedunder an atmospheric atmosphere whose peak temperature is set to rangefrom about 100° C. to 250° C. At this time, among materials mixed in theIC chip coating material 25A, a solvent for dispersing alumina powdercontained in the alumina sol solution used as a fixing material into asolution and an ethylene glycol serving as an organic solvent for makingthe IC chip coating material 25A a paste are evaporated. As a result,fine coloring metal oxide particles, mica serving as the flat fineparticles of the composite oxide and metal oxide particles (alumina)serving as a fixing material remain as the IC chip coating material.

Due to the mixture of particles of a different particle size in thecoating material layer 25, it is possible to relax the stress from thethermal expansion caused during the drying process and further toprevent a breakdown of the wire or a crack in the IC chip coatingmaterial 25A. Further, since gas components generated from the diebonding paste 23A are evaporated together with an evaporating element inthe IC chip coating material 25A during the drying process, gas ishardly generated from the die bonding layer 23 after the formation ofthe coating material layer 25 is completed. Moreover, the gas is hardlygenerated during the manufacturing process of the fluorescent displaydevice, which is performed at a temperature higher than or equal to 400°C.

After the IC chip coating material 25A is dried, a box-shaped container22 is sealed at about 480° C. to be fixed on the anode plate 11. Next,by exhausting gas in the fluorescent display device through a gasexhaust line (not illustrated), a high vacuum state is achieved.Thereafter, the gas exhaust line is sealed, thereby completing thefluorescent display device 1.

In the first preferred embodiment, when the IC chip coating material 25Amade of the aforementioned materials (1) to (4) is coated, a compositionthereof (in case of a total amount being 100 wt %) is as follows:

(1)+(2): 60 to 70 wt % (added at a ratio of (1):(2)=4:1);

(3): 5 to 20 wt %; and

(4): 10 to 35 wt %.

Meanwhile, a composition of the coating material layer formed throughthe drying process is as follows:

(1)+(2): 97 to 99 wt %;

(3): 1 to 3 wt %; and

(4): 0 wt %.

Accordingly, it can be understood that a solvent for dispersing aluminapowder contained in the alumina sol solution used as a fixing materialinto a solution and an organic solvent for making the IC chip coatingmaterial 25A a paste are evaporated during the drying process.

As shown in FIG. 6, after coating another IC chip coating material 25Bof the present invention and the conventional IC chip coating materialincluding alumina on Al-wirings having a 30 μm gap (on an area within adistance of 10 mm that is coated with the IC chip coating material(hereinafter, refer to as a “facing distance”)), the drying processes ofthe present IC chip coating material and of the conventional IC chipcoating material were performed under the atmosphere whose peaktemperatures were set to range from about 100° C. to 250° C. and to beabout 480° C., respectively. The IC chip coating material 25B isidentical to IC chip coating material 25A, excepting that the black finemetal oxide particles including Fe, Cr and Mn is replaced with blackfine metal oxide particles including Fe and Cr as a main componentthereof (Fe₂O₃: about 53%, Cr₂O₃: about 47%). Further, a leak testbetween wires was performed by applying a voltage of 100 V between thewirings having a 30 μm gap (facing distance being about 10 mm) in avacuum container.

As a result, the IC chip coating material 25B of the present inventionhas been found to have a resistance in the order of 10⁴ MΩ to 10⁵ MΩrange, which is substantially same as that in the order of 10⁵ MΩ rangeof the conventional coating material including alumina as a maincomponent thereof. This indicates that a current showing an insulatinglevel between parallel wires of the IC chip ranges from 0.5 μA to 1.0μA, which falls within a reference standard range required by thestandard (the standard current level flowing between the wires is about1 μA when a voltage of 100 V is applied).

The IC chip coating materials 25A and 25B were applied to the Al-wiringsas in the test setup of FIG. 6 (i.e., with the wiring gap of 30 μm andthe facing distance of 10 mm). Further, as shown in FIG. 7, IVcharacteristics between the Al-wirings were performed by applying avoltage ranging from about 0 V to 130 V. From the result, it can be seenthat in case of using the IC chip coating material 25B without havingMn, the current begins to increase at critical voltage of 20 V andcontinues to rise from about 0.3 μA to 1.2 μA as the voltage increasesacross the medium voltage range from about 60 V to 130 V. On the otherhand, in case of the IC chip coating material 25A including Mn that ismore stable against oxidation and deoxidation compared to Fe and Cr asshown in FIG. 8, the current is smaller than or equal to 0.2 μA even inthe medium voltage range as shown in FIG. 7, which is within thereference standard value.

In the fluorescent display device 1 described above, since a low boilingpoint solvent is evaporated during the drying process, gas is hardlygenerated from the die bonding layer 23 after the formation of thecoating material layer is completed. Accordingly, the IC chip 16 and itsneighboring area can be coated with the IC chip coating material 25A. Asa result, it is possible to prevent a short-circuit caused by theconductive foreign substances or the like or defects (a false operationcause by external light and a scattering of Ba arranged directly below afilament-shaped cathode) developed at an exposed portion of the IC chip16.

Moreover, in an adhering process of the IC chip coating material 25Acoated on the IC chip 16, it is preferable to set a drying temperaturepreferably to range from about 100° C. to 250° C. Consequently, anoperating cost can be reduced and the coating material layer 25 can beformed without applying any unnecessary load to the IC chip.

Furthermore, by adding black metal oxide including coloring Fe, Crand/or Mn as a main component thereof to the IC chip coating material25A, a color tone similar to that of the black insulating layer 26 canbe obtained, thereby making it possible to provide a fluorescent displaydevice having no contrasting color tone difference.

By mixing, in addition to the fine coloring metal oxide particles, finemetal oxide particles having a composition identical to or differentfrom that of the aforementioned fine metal oxide particles and also of amean particle size and/or a shape different from that of theaforementioned fine metal oxide particles; and/or flat fine particles ofthe highly insulating composite oxide such as mica or the like, the ICchip coating material 25A can have a reduced elasticity and a stress dueto a thermal expansion during the drying process can be reduced, therebymaking it possible to prevent cracks of the coating material layer 25.

Besides, by adding Mn-based oxide as black fine metal oxide particles tothe IC chip coating material 25A, it is possible to minimize the leakcurrent even in a medium driving voltage range in comparison to the ICchip coating material for the conventional fluorescent display device.

Second Preferred Embodiment

In accordance with a second preferred embodiment, instead of the IC chipcoating material used in the first preferred embodiment, there is usedan IC chip coating material for a fluorescent display devicemanufactured based on following compositions. Also, a fluorescentdisplay device is manufactured by using a method identical to that ofthe first preferred embodiment except the IC chip coating material. Evenin case of using the IC chip coating material manufactured based on thefollowing compositions, the same effects as those of the first preferredembodiment can be achieved:

(1) fine Al oxide particles including Al as a main component thereof,whose particle size is about 0.3 μm: 55 g,

(2) flat fine particles of a composite oxide, i.e., mica whose particlesize is about 25 μm: 15 g,

(3) alumina sol: 10 g, and

(4) ethylene glycol: 20 g.

Third Preferred Embodiment

In accordance with a third preferred embodiment, instead of the IC chipcoating material used in the first preferred embodiment, there is usedan IC chip coating material manufactured based on followingcompositions. Also, a fluorescent display device is manufactured byusing a method identical to that of the first preferred embodimentexcept the IC chip coating material. Even in case of using the IC chipcoating material manufactured based on the following compositions, thesame effects as those of the first preferred embodiment can be achieved:

(1) fine Al oxide particles including Al as a main component thereof,whose particle size is about 0.3 μm: 50 g,

(2) fine Al oxide particles including Al as a main component thereof,whose particle size is about 5 μm: 20 g

(3) TOG: 15 g, and

(4) ethylene glycol: 15 g.

Fourth Preferred Embodiment

In accordance with a fourth preferred embodiment, instead of the IC chipcoating material used in the first preferred embodiment, there is usedan IC chip coating material manufactured based on followingcompositions. Also, a fluorescent display device is manufactured byusing a method identical to that of the first preferred embodimentexcept the IC chip coating material. Even in case of using the IC chipcoating material manufactured based on the following compositions, thesame effects as those of the first preferred embodiment can be achieved:

(1) black fine metal oxide particles including Fe, Cr, and/or Mn as amain component thereof, whose particle size is about 3.5 μm: 50 g,

(2) black fine metal oxide particles including Fe, Cr, and/or Mn as amain component thereof, whose particle size is about 25 μm: 10 g,

(3) alumina sol: 10 g, and

(4) ethylene glycol: 30 g.

Fifth Preferred Embodiment

In accordance with a fifth preferred embodiment, instead of the IC chipcoating material used in the first preferred embodiment, there is usedan IC chip coating material manufactured based on followingcompositions. Also, a fluorescent display device is manufactured byusing a method identical to that of the first preferred embodimentexcept the IC chip coating material. Even in case of using the IC chipcoating material manufactured based on the following compositions, thesame effects as those of the first preferred embodiment can be achieved:

(1) black fine metal oxide particles including Fe, Cr, and/or Mn as amain component thereof, whose particle size is about 3.5 μm: 40 g,

(2) black fine metal oxide particles including Fe, Cr, and/or Mn as amain component thereof, whose particle size is about 20 μm: 20 g+finecomposite oxide particles whose particle size is about 25 μm: 10 g,

(3) alumina sol: 10 g, and

(4) ethylene glycol: 20 g.

Sixth Preferred Embodiment

In accordance with a sixth preferred embodiment, instead of the IC chipcoating material used in the first preferred embodiment, there is usedan IC chip coating material manufactured based on followingcompositions. And, also, a fluorescent display device is manufactured byusing a method identical to that of the first preferred embodimentexcept the IC chip coating material. Even in case of using the IC chipcoating material manufactured based on the following compositions, thesame effects as those of the first preferred embodiment can be achieved:

(1) black fine metal oxide particles including Fe, Cr, and/or Mn as amain component, whose particle size is about 3.5 μm: 53 g,

(2) flat fine particles of a composite oxide, i.e., mica whose particlesize is about 25 μm: 10 g,

(3) alumina sol: 10 g, and

(4) octanediol: 22 g+dimethylformamide: 5 g.

In accordance with an IC chip coating material of the present invention,since metal oxides of a mean particle size and/or a shape different fromthat of the added fine metal oxide particles are mixed, the coatingmaterial is of a reduced elasticity and a stress due to a thermalexpansion caused during the drying process is also reduced. Further, ifthe metal oxide particles are of the same composition, the effects arefurther enhanced. Furthermore, if flat fine particles of the compositeoxide are mixed with the metal oxide particles, the effects are muchfurther enhanced.

A process for coating and adhering the IC chip coating material to makea coating material layer is completed only by the drying processperformed at about 100° C. to 250° C. Accordingly, an operating cost canbe reduced and, further, the coating material layer can be formedwithout applying an unnecessary load to the IC chip. In addition, incase of the coating material layer, after the manufacturing process ofthe fluorescent display device is performed at a temperature higher than400° C., the metal alkoxide is decomposed and a solid content isexclusively coated as the coating material layer. Consequently, it ispossible to protect the coated portion from the short-circuit in the ICchip due to the conductive foreign substances or the like or defectsgenerated at an exposed portion of the IC chip (a false operation causedby external light and electrons emitted from a filament and effects ofBa scattered from the filament).

Besides, by adding black metal oxide particles including coloring Fe, Crand/or Mn as a main component thereof to the coating material layer, acolor tone similar to that of a black insulating layer can be obtained,thereby making it possible to provide a fluorescent display devicehaving a very little color tone difference. Furthermore, by adding whitemetal oxide particles including coloring Al to the coating materiallayer, a color tone similar to that of a white insulating layer can beobtained, thereby making it possible to provide a fluorescent displaydevice having a very little color tone difference.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modification may be made without departing fromthe scope of the invention as defined in the following claims.

1. A vacuum fluorescent display device comprising: an IC chip, wherein the IC chip is at least partially coated by a coating material layer which includes: first metal oxide particles for coloring the coating material layer, the first metal oxide particles including particles of alumina; second metal oxide particles serving as a fixing material, the second metal oxide particles being formed from an alumina-based metal alkoxide; and flat composite oxide particles including particles of mica, wherein the first metal oxide particles have a mean particle size different from that of the second metal oxide particles.
 2. The vacuum fluorescent display device of claim 1, wherein the coating material layer for coating the IC chip is white.
 3. The vacuum fluorescent display device of claim 1, wherein the first and second metal oxide particles consist of alumina.
 4. The vacuum fluorescent display device of claim 1, wherein the flat composite oxide particles consist of the particles of the mica.
 5. The vacuum fluorescent display device of claim 1, wherein the mean particle size of the first metal oxide particles is about 0.3 μm.
 6. The vacuum fluorescent display device of claim 1, wherein a mean particle size of the flat composite oxide particles is about 25 μm.
 7. The vacuum fluorescent display device of claim 1, wherein the first metal oxide particles have a shape different from that of the second metal oxide particles.
 8. The vacuum fluorescent display device of claim 1, wherein a mean particle size of the flat composite oxide particles is different from these of the first and the second metal oxide particles.
 9. The vacuum fluorescent display device of claim 1, wherein the flat composite oxide particles have a shape different from these of the first and the second metal oxide particles.
 10. The vacuum fluorescent display device of claim 1, wherein the flat composite oxide particles serve to reduce a stress of the coating material layer due to a thermal expansion when the coating material layer is formed.
 11. The vacuum fluorescent display device of claim 1, wherein the flat composite oxide particles serve to reduce an elasticity of the coating material layer.
 12. The vacuum fluorescent display device of claim 1, wherein the coating material layer serves as a layer protecting the IC chip from the surroundings thereof.
 13. The vacuum fluorescent display device of claim 1, further comprising: one or more bonding wires each of which is connected to an electrode of the IC chip.
 14. The vacuum fluorescent display device of claim 3, wherein the flat composite oxide particles consist of the particles of the mica.
 15. The vacuum fluorescent display device of claim 7, wherein a mean particle size of the flat composite oxide particles is different from these of the first and the second metal oxide particles.
 16. The vacuum fluorescent display device of claim 8, wherein the flat composite oxide particles have a shape different from these of the first and the second metal oxide particles.
 17. The vacuum fluorescent display device of claim 9, wherein the IC chip and the bonding wires are entirely coated by the coating material layer.
 18. The vacuum fluorescent display device of claim 15, wherein the flat composite oxide particles have a shape different from these of the first and the second metal oxide particles.
 19. The vacuum fluorescent display device of claim 1, wherein a mean particle size ratio of the first metal oxide particles to the flat composite oxide particles is set to be 1:5 or more.
 20. The vacuum fluorescent display device of claim 1, wherein an amount of the flat composite oxide particles is about 20% of a total amount of the first metal oxide particles and the flat composite oxide particles in the coating material layer. 